Microsoft 365 activation suddenly fails with "Unknown Error 0x0" on macOS Big Sur 11.7.11

ben 0 Reputation points
2026-07-25T02:33:10.9333333+00:00

I have been using a iMac Retina 5K, 27-inch, Late 2014, macOS Big Sur 11.7.11. It could not be upgraded to higher version.

Suddenly, the microsoft 365 office requests activation, despite a valid subscription till 07 Oct 2026.

I logged into my microsoft ID and the activation fails. I deleted and downloaded office version 16.77 from microsoft website again and still not works.

Microsoft 365 and Office | Install, redeem, activate | For home | MacOS
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  1. EmilyS726 256K Reputation points Independent Advisor
    2026-07-25T03:04:33.1433333+00:00

    Hello,

    If your macOS is below 12, Office products will now enter reduced functionality mode. In other words, the OS is too old to receive the licensing update the Office now requires. Sorry.

    This is an update that occured on July 13th and Microsoft shared it here: https://support.microsoft.com/office/update-microsoft-365-or-office-on-your-macos-or-ios-device-f418ae5d-bb5f-4078-b3d9-9340f5dd084e?apid=ets

    If your device cannot update its OS to at least 12, your options will be: Use the web version or an alternative like LibreOffice. And you want to cancel your subscriptions.

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